Here’s another example of a sign that inserts an apostrophe in the plural of a word that doesn’t contain an apostrophe in standard English spelling. The word is milkshake’s, standardly written as milkshakes.
I’ve written before about an intrusive (and normatively ‘incorrect’) apostrophe in the word milkshake. Panini’s apostrophes – Language Miscellany There, milkshake’s followed a borrowed word panini’s whose plural form is likely to cause some anxiety and uncertainty to many writers. But in this latest case, the sign doesn’t contain any other plural form that could cause so much uncertainty or anxiety.
The latest example is at a café in southeast London. Oddly and perhaps revealingly, the other side of the sign (not shown here) displays the word milkshakes, written without an apostrophe.